The present invention relates generally to electric vehicles and hybrid electric vehicles that make use of regenerative braking. In particular, the present invention relates to controlling a mild regenerative braking torque applied when the vehicle is coasting to simulate the feeling of a vehicle having an internal combustion engine when the driver has let off the throttle when the vehicle is either on a flat grade or the vehicle is driving down a hill.
Conventional automobiles which are driven by an internal combustion engine provide an engine braking effect when the vehicle is coasting. In particular, when the driver of a conventional vehicle has let off the throttle while the vehicle is either on a flat grade or driving down a hill, the internal combustion engine tends to apply a braking force (often called engine braking) through the transmission to the traction wheels of the vehicle. In particular, the braking force applied by the engine is due to the fact that the engine slows down when the accelerator pedal is released so that the engine output shaft applies a resistance torque to the transmission which is therefore transmitted to the drive wheels. The majority of the driving public has become accustomed to the feel of a vehicle which has engine braking during coast-down.
Accordingly, it is desirable in the development of electric and hybrid electric vehicles to provide a similar feel to the driver when the driver lets off the throttle when the vehicle is either on a flat grade or driving down a hill in order to increase the acceptance of these vehicles. Specifically, the present invention is directed toward providing a mild regenerative braking torque when the vehicle is coasting to simulate the feeling of the internal combustion vehicle. The objective of the present invention is to control or maintain the vehicle speed when coasting down a hill by monitoring the vehicle speed and varying the coast-down regen torque being applied.
The present invention solves the problem of adding a xe2x80x9clowxe2x80x9d position on the PRNDL display where a single speed gear box for an electric vehicle does not have a lower gear. The present invention has the advantage of letting the driver be able to drive as normal down a long steep hill by letting the foot off the throttle to adjust the vehicle speed. Otherwise, the driver has to shift the gear selector to a low position (if available) or use the brakes, which end up losing the usable energy as friction heat. The present invention also has the advantage of prolonging the life of the friction brake system while extending the driving range of electric vehicles and hybrid electric vehicles by converting the braking energy into stored electric energy.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.